The spokesman said police had been told the incident involved a conveyor belt but that hadn’t been confirmed.Police told news.com.au they were trying to get more details about what occurred. A spokesman said officers were called to the major tourist attraction and were now dealing with a “critical incident”.

He also could not confirm reports a person had been killed.

A Queensland Workplace Health and Safety spokesman said they had been informed of the incident.

Preliminary reports it may have been an industrial accident on a ride undergoing repair were false, he said.

“The early indications we have is that the ride was operating at the time of the incident,” he said.

Dreamworld has been contacted for further details on the incident.

US Olympic gold medallist Matthew Centrowitz tweeted he just got off the ride that the accident happened on.

“Our thoughts are with the families of those affected – and the emergency staff in attendance.”

The Thunder River Rapids Ride is currently Australia’s only river rapids ride and opened on December 11, 1986, reports the Gold Coast Bulletin.

Riders board one of several six-person circular rafts.

The raft is dispatched and the riders travel back past the ride’s queue and into a cave.

Upon exiting the cave, riders experience the main rapids section of the ride. This section runs alongside a large water catchment which powers both the Thunder River Rapids Ride and the Rocky Hollow Log Ride.

Park officials say a “malfunction” caused two people to be thrown from the ride, while two others were trapped inside. The victims were aged between 30 and 40.

Police were called to the scene following reports that one of the six-seat Tyre-style carriages had flipped on the conveyor belt.

Dreamworld was closed following the incident. The park says it is working closely with police, emergency services and authorities to investigate the incident.

Part of a a statement released by the park read, “Dreamworld is working as quickly as possible to establish the facts around the incident and is working closely with emergency authorities and police to do this. Dreamworld’s focus and priority is with the families of those involved in this tragedy and will be providing an update to the public as soon as information becomes available.”

Dreamworld bills itself as Australia’s biggest theme park with more than 50 rides and attractions.

The incident comes about six months after a near-drowning on Dreamworld’s popular log ride. Back in April, a man fell out of the ride and was treated by the theme park’s medical staff after he swallowed water and suffered head cuts.

Other tragic incidents at amusement parks around the world include eight teenagers killed in a 1984 fire at the Six Flags Great Adventure amusement park in New Jersey, US; six people killed by a failed simulated rocket launch in Shenzhen, China, in 2010 and five children killed when the Battersea Park Big Dipper malfunctioned in Britain in 1972.